Conventional devices and methods are used for producing precise microholes in workpieces by using laser beams, where the holes may have a diameter smaller than 250 μm.
In laser beam drilling, in particular using short-pulse lasers with the conventional devices, melt burrs are formed in workpieces made of a metallic material on the laser beam entrance side of the workpiece which must be deburred in an afterworking operation. Furthermore, a melt film is formed in the hole, i.e., on the peripheral surface of the hole, which must also be removed subsequently, but there must not be any unwanted loss of material at the edges of the hole and/or blockage of the hole.
In the field of fuel injection, for example, there is a growing demand for conical holes, e.g., in nozzles, so that the laser beam entrance opening (fuel outlet) usually requires a smaller diameter than the laser beam exit opening (fuel inlet). Conventionally, to produce these holes having a desired conicity, the workpiece may be tilted in relation to the laser beam and/or the machining strategy, i.e., the parameters of the laser beam, may be adjusted accordingly. It has been found that the conicity which is achievable with the conventional methods and is definable on the basis of the k factor is relatively limited, depending on the diameter of the hole.